In the fields of optical measurement and opto-electronics, a wavelength tunable light source capable of changing the wavelength over a wide band has become increasingly important.
In the case of a semiconductor laser, which is used as a conventional wavelength tunable light source, the variable wavelength band is limited to the gain band, and therefore the wavelength cannot be greatly changed. For example, a method for changing the wavelength by rotating a diffraction grating also has been proposed. However, this method requires mechanical sweeping and cannot achieve high-speed wavelength conversion.
To solve these problems, as a light source capable of changing the wavelength without adjustment of the optical system, Patent Document 1 proposes an apparatus that includes a laser light source for generating an ultrashort optical pulse on the order of femtoseconds (fs), a regulator for regulating the wavelength characteristics of the generated ultrashort optical pulse, and an optical fiber for receiving the ultrashort optical pulse whose characteristics have been regulated by the regulator.
The wavelength tunable light source of Patent Document 1 uses the soliton effect that is the interaction between self-phase modulation and wavelength dispersion, and thus allows the optical pulse to be an ideal soliton pulse in the optical fiber. As the optical pulse propagates in the optical fiber, the pulse wavelength shifts to the long wavelength side due to the soliton self-frequency shift effect of the optical fiber. Moreover, the amount of wavelength shift is controlled by adjusting the length of the optical fiber and the intensity of the ultrashort optical pulse input to the optical fiber, so that the ultrashort optical pulse to be generated can have a desired center wavelength.